question

A typical 24v nominal battery charges between 28.4 and 29.2v, just like a typical 12v nominal battery charges at 14.2-14.6v

@Jay Kote 1. 24v is the nominal battery (system) voltage, ie 12v/24v/36v/48v. system voltage.

2. the mppt is rated for 20a output. 20a x battery voltage gives the watt output. Ie 20a x 27.6v gives 552w.

3. the mppt will only charge the batt up to the voltage set for absorption. The system voltage is a separate thing.

4. As above.

5. As per the mppt manual you need the pv voltage to be higher than the battery voltage by 5v. Panel Vmp is the voltage where the panel produces the highest watt output. Pv voltages above or below Vmp will result in less pv current (and lower output watts P=IxV).

So please don't ask for specifications of solar panel Unfortunately these are system design questions. You need to know the panel specs to ensure that you have enough voltage for the mppt to operate correctly.

Also be aware that panel voltage specs will vary with temperature. Also if you are usung lead acid batteries, their charge voltage will vary with temperature.

Please clarify what you mean by "nominal" system voltage? Because the answer to (1) is incongruent to (2) and the specification to the 100/20.

Part 1

Let me explain.

The max wattage for a 100/20 in a 12V system is 290W, per manual. And 580W for a 24V system. Per your explanation in (2), 20A*12 = 240W not 290W. And 20A*24V = 480W not 580W. The 290W and 580W are in the 100/20 manual.

The inconsistency then is either (a) 12V does not mean "12V", but 14.5 so to yield 290W and (b) 24V does not mean 24V, but 29V.

So why does the manual state 290W and 580W?

Part 2

This is not about any specific panel. This question is what is the ideal voltage from a hypothetical panel relative to battery voltage for the MPPT. If it will help your thinking, imagine you have an ideal DC voltage/current source which you can tune to ensure the MPPT is going to do best and most efficient.

For a battery that is low of 20V and high of 24V (as measured on a volt meter, not "nominal", what is the ideal setting of the input voltage and current into the MPPT which you can regulate on your ideal DC power supply?

Part 3

Case 1: battery voltage 20V what is the ideal Voltage 1 and Ideal Current 1 setting on the DC supply so to allow MPPT to achieve Max efficiency?

Case 2: battery voltage 24V Voltage 2? Current 2?

Case 3: Consider then the situation that the battery voltage is 20, and the MPPT is receiving a voltage of 38V (exceeds the 5V) and there is 10A going into the MPPT, what amps should the MPPT deliver? Same question, but assume battery at 24V. You can assume the the battery SOC is such that in all cases the MPPT is in "Bulk" and the absorption is only 1/10 of volt lower.

General Question:

Where is Victron specification of this curve. I see on another post someone using a curve from another MPPT manufacturing and assuming they would be the same -- big leap of faith. Victron could be better or worse.

Is this forum a user forum only? Where are the Victron engineers who should be able to answer all these questions with specificity to Victron?

@Jay Kote

Please clarify what you mean by "nominal" system voltage? Just because a 24v battery is discharged to 20v, or fully charged to 29v does not make it either a 20v or 29v battery. It is a 24volt battery. (24v system voltage)

Per your explanation in (2), 20A*12 = 240W not 290W. And 20A*24V = 480W not 580W. The 290W and 580W are in the 100/20 manual. Your maths is correct. Also note the pv power figures in the manual are "Nominal PV power", not minimum or maximum figures.

The inconsistency then is either (a) 12V does not mean "12V", but 14.5 so to yield 290W and (b) 24V does not mean 24V, but 29V. So why does the manual state 290W and 580W?
The 14.5v/29v battery charge voltage is used as an awful lot of batteries charge up to those voltages.

This is not about any specific panel. This question is what is the ideal voltage from a hypothetical panel relative to battery voltage for the MPPT. From the manual, The PV voltage must exceed Vbat + 5V for the controller to start. Thereafter the minimum PV voltage is Vbat + 1V. Ideally I would recommend that the panel Vmp would be at least 5v above the batteries full charge voltage. For the 29v battery that would be 34v to ensure the mppt starts, and re-starts should bad clouds send the mppt to sleep (it happens) or the mppt gets disconnected from the battery (also happens).

Not much point if the battery only gets charged to 28v, charging gets interrupted, and your panel is only at 30v. Charging will not resume until the battery drops to 23v, or the panel voltage goes to 33v.

imagine you have an ideal DC voltage/current source which you can tune to ensure the MPPT is going to do best and most efficient. Solar panels are far from an ideal source. When the sun is off angle, the power drops. When they get cold, their voltage/power goes up. When they get hot, their voltage/power goes down. Any shade/shadows drastically reduces power, as the panel volts/current gets mucked with.

As long as the pv volts is +5v over the battery voltage, the mppt efficiency is good. Higher pv volts will be a little bit more efficient. Efficiency drops off at low (and presumably high) power levels.

battery voltage 20V what is the ideal Voltage 1 and Ideal Current 1 setting on the DC supply so to allow MPPT to achieve Max efficiency?

Using a DC power supply is not recommended, do so at your own risk.

Consider then the situation that the battery voltage is 20, and the MPPT is receiving a voltage of 38V (exceeds the 5V) and there is 10A going into the MPPT, what amps should the MPPT deliver? Simple maths, power in = power out (minus some small loss) V x A = P > P / V = A. the MPPT is in "Bulk" and the absorption is only 1/10 of volt lower. With Victron chargers, the bulk and absorption is the same value.

Where are the Victron engineers who should be able to answer all these questions with specificity to Victron? Most of what you are asking is basic maths.